A wide range of synthetic base stocks have been developed to alleviate the deficiencies of petroleum base stocks, for example, polyalphaolefins, esters, silicones, perfluorinated polyethers, and the like. For specific applications, in particular for liquid space lubricants, materials are required which exhibit extremely low volatility and specific viscosity-temperature properties enabling them to perform under extreme conditions. The perfluoroalkylethers, a product of Montedison described in U.S. Pat. No. 3,715,378, although meeting the above criteria, present corrosion problems due to the presence of fluorine. The monosilahydrocarbons described, for example, by C. E. Snyder et al., ASLE Transactions, Vol. 25, No. 3, pp. 298-308 (1982), have been shown to be superior to synthetic hydrocarbons, such as the polyalphaolefins, in viscosity-temperature properties, oxidative stability, and especially thermal stability, while additionally having advantages over silicones (polysiloxanes) in lubricity and bulk modulus. It is evident that incorporation of the silicon atom into the hydrocarbon skeleton can improve the utility of the structure for synthetic lubricant purposes.
However, the desirable effects of the silicon atom in the monosilahydrocarbons of the prior art become attenuated as the alkyl chains therein are increased beyond a certain length. Monosilahydrocarbons containing, for example, 90 or more carbon atoms would almost certainly be solids, not fluids, at room temperature. The molecular weight increase is mandatory to attain the required low volatility and sufficiently high viscosity to permit operation at elevated temperatures.
The trisilahydrocarbons described by U.S. Pat. No. 4,788,312 alleviated, to a high degree, the limitations inherent in monosilahydrocarbons and provided base fluids for certain applications. However, for very specific uses, where low volatility and particular viscosity characteristics are required, these materials are inadequate. A new class of silahydrocarbons is thus necessary which will exhibit the viscosity-volatility-temperature properties not achievable by the type of compositions currently known. It is further desirable for this new class of silahydrocarbons to be prepared from readily accessible raw materials. It is additionally desirable to have available relatively simple silicon-containing chemical intermediates, which, by the proper choice of reagents and conditions, could be converted into numerous silahydrocarbon structures designed to have properties suitable for specific applications. Our invention satisfies all these objectives.
We are not aware of the use of tetrasilahydrocarbons or pentasilahydrocarbons of our invention in synthetic lubricant applications. These tetrasilahydrocarbons and the chemical intermediates employed in their preparation and disclosed herein are, to the best of our knowledge, new chemical compounds previously unknown.